Feed bushing for single screw extruder
A feed bushing for single screw extruder for the plasticizing extrusion of plastics under a high inertia resistance comprising an outer casing, a grooved bushing twin screw extruder enclosed in the outer casing, and a cooling system. The groove bushing sheet production extruder is assembled from a tubular grooved inset and a tubular reinforcement surrounding the grooved inset, the inset being shrink-fitted into the reinforcement with such a high shrinkage allowance that the inset is prestressed for pressure by the reinforcement for withstanding the maximum forces of inertia of the screw received in the grooved bushing. The grooved inset of the grooved bushing is made of cemented carbide, a metal oxide or other extremely hard and wear-resistant material. The reinforcement element is made of high-strength ductile steel.
In accordance with the invention, this object is accomplished in that the grooved bushing is assembled from a tubular grooved inset and a tubular reinforcement which surrounds the grooved inset, the grooved bushing having the inset and reinforcement then being enclosed in an outer casing.
The grooved bushing is formed of an extremely wear-resistant grooved inset which is shrink-fitted into a reinforcement through a press fit that is not adapted to be disassembled. The extremely wear-resistant grooved bushing thus is removable and replaceable. The grooved inset is made of a hard, wear-resistant material. The reinforcement is made of a high-strength, tough steel which will withstand very high tensile stresses.
The shrinkage allowance for the press fit between grooved inset and reinforcement is set so high that the grooved inset, made of a brittle and hard material, is always prestressed for pressure by the high-strength reinforcement at the maximum melt pressures in the screw. The grooved inset therefore cannot fracture as a result of the buildup of pressure in the screw. The grooved bushing with the reinforcement is installed in the outer casing. The fit between the reinforcement and outer casing will depend on the loading and use made of the extruder:
1. In the case of an extruder subjected to normal loads, the fit is made with very little clearance, that is to say, a small shrinkage allowance. With such a fit, the grooved bushing can always be removed without the outer casing having to be destroyed.
2. In the case of special extruders subjected to very high loads, or in the processing of extremely high-viscosity plastics, the melt pressure in the extruder screw rises to such extremely high levels that the simple reinforcement will not absorb it. In that case, the grooved inset must be prestressed still higher through double reinforcement by means of the reinforcement and of the outer casing. Such double reinforcement permits very high prestressing to be produced in the grooved inset.
A feed bushing single screw extruder so designed is able to withstand operating pressures or momentary overloads of up to 4000 kg/cm 2 .